Measurements of Unity Gain Cutoff Frequency and Saturation Velocity of a GaN HEMT Transistor

The measured intrinsic saturation velocity (v/sub si/) of carriers in a gallium nitride (GaN) high electron mobility transistor (HEMT) is very much lower than that predicted using Monte Carlo simulation. A novel method of extraction of the intrinsic saturation velocity (v/sub si/) of carriers has been developed utilising the deembedded s-parameters, thus enabling the calculation of v/sub si/ over a wide range of bias conditions. The method is equally applicable for gallium arsenide (GaAs) and indium phosphide (InP) based transistors. The measurements indicate for GaN-based HEMT a maximum deembedded saturation velocity of 1.1/spl times/10/sup 5/ m/s close to the pinchoff voltage (V/sub P/). It was found that self-heating had only a weak effect on the saturation velocity up to junction temperatures approaching 140/spl deg/C above ambient.